In order to prevent a fall accident from a bed, there is a system that assists watching over a patient in a hospital or a nursing facility. Patent Document 1 proposes a system that detects a patient's head from an image captured by a camera installed obliquely above the bed, and determines raising-up action when the head exceeds a boundary line set on the bed. Patent Document 2 proposes a system that detects a moving direction of the patient from the camera image, and determines a current state of the patient based on the combination of the moving direction of the patient and the past state (going-to-bed state/raising-up state/getting-out-of-bed state/absent state).